The present invention relates to an organic binder for shaping ceramic used to produce the shaped product, namely green sheet consisting of ceramic precursor when shaping so called ceramic including alumina from the viewpoint of low pollution, resource saving and safety; it related especially to the organic binder for shaping ceramic of water system excellent in removability of binder, its production method and product employing the same.
(i) Conventionally, such an organic binder as butylal resin and acrylic acid ester is generally used as ceramic binder. This binder is dissolved or dispersed in such organic solvent as alcohol, ketone, chloride system solvent, aromatic solvent, is mixed with fine ceramic powder, and is kneaded by the ball mill or similar means for a long time to be made into a slip form. After being degassed, this is cast into sheets having a specified thickness by the doctor blade method or reverse quarter method, and heated and dried on such a material as polyester film to be made into green sheets. PA1 (ii) Regarding the ceramic water-soluble binder, the watersoluble polyvinyl acetal having an acetalization degree of 10 mol percent or less is disclosed in the Japanese Patent Application Laid-open NO. 56-76405, and the cold water soluble polyvinyl acetal having an acetalization degree of 10 to 30 mol percent or less is disclosed in the Japanese Patent Application Laid-open NO. 1-29408-1989, while the denaturated polyvinyl alcohol (PVA) having the side chain of hydrophobic group or specific ionic hydrophilic group uses as water system organic binder is disclosed in the Japanese Patent Application Laid-open NO. 59-156959. PA1 (iii) The water soluble acrylic acid ester system binder is disclosed in the Japanese Official Patent Gazette 1-53233, the Japanese Official Patent Gazette 1-44668 and the Japanese Patent Application Laid-open NO. 1-286955. Ammonia, trialkylamine such as trimethylamine, and amine such as dimethylamine alcohol, monoethanolamine are added to the methacrylic acid ester or acrylic acid ester copolymer having the carboxyl group (hereinafter referred to as "(meth)acrylic acid copolymer") -the (meth)acrylic acid ester copolymer consisting of copolymerized (meth)acrylic acid--thereby achieving neutralization (pH adjustment). PA1 (iv) Emulsion binders which are produced by emulsification and polymerization of vinyl monomer by the surfactant and which are neutralized (pH-adjusted) by ammonia using the (meth)acrylic acid are disclosed in Japanese Patent Application Laid-open NO. 60-180955, Japanese Patent Application Laid-open NO. 60-180956, Japanese Patent Application Laid-open NO. 61-151060 and Japanese Patent Application Laid-open NO. 1-286955, while those having crosslinking structure are disclosed in the Japanese Patent Application Laid-open NO. 63-260855. PA1 (v) The Japanese Patent Application Laid-open NO. 3-131604 discloses the swollen substance comprising (a) alpha-olefin polymer, (b) single (meth)acrylic acid or (meth)acrylic acid monomer and stylene monomer, and (c) polymerization initiator is dispersed, for example, in the water system medium containing such a polymerization dispersant as water soluble high polymer polyvinyl alcohol and is subjected to suspension polymerization to be formed into the binder. PA1 (vi) The Japanese Patent Application Laid-open NO. 59-128266 discloses the complex organic binder for shaping ceramic containing 1 to 1,000 parts by weight of hydrophobic high polymer (a) for 100 parts by weight of the water soluble high polymer.
On the other hand, (vii) the Japanese Patent Application Laidopen NO. 59-995 and Japanese Patent Application Laid-open NO. 60-254697 disclose the ceramic circuit board production method, where polymethyl methacrylate resin and polymethacrylic acid ester resin as the binding including the pyrolytic polymer type resin are disclosed.
For the binder mentioned in said (i), however, butyl alcohol, isopropyl alcohol, trichloroethylene, toluene, etc. are used as organic solvent. However, they have problems in explosiveness by ignition, hazard of causing fire, and offensive odor in molding and drying--especially, the halogen system solvent involving such pollution problems as environmental pollution by evaporative gas and hazards to human bodies; solution of these problems requires installation of an explosion proof device, exhaust treatment equipment and solvent recovery equipment.
The cases of said (ii) and (iii) have the disadvantage that characteristics of the ceramic green sheet are subjected to variation because water soluble has a great hygroscopicity. The case of said (iv) has the disadvantage that the ceramic green sheet using emulsion having carboxyl group features a weak tensile strength and is inferior in glossiness and flatness.
Furthermore, all binders involve such problems as inferior removability of binders and inferior strength of the ceramic sheet and ceramic circuit board after firing.
The case of said (v) features poor mutual solubility between components (a) and (b) is poor and inferior mechanical characteristics of the ceramic precursor composition. Use of polymers featuring poor thermal decomposition such as alphaolefin polymer and polyvinyl alcohol involves such problems as inferior removability of binders and inferior strength of the ceramic, ceramic sheet and ceramic circuit board after firing.
The case of said (vi) provides a method by which hydrophobic high polymer latex produced as water system dispersion substance by emulsification and polymerization is dissolved in water soluble high polymer solution. Since the water soluble high polymer contains a great deal of high polymers featuring poor thermal decomposition, it is important to minimize the amount to be added if the water soluble high polymer is to be used as binder. Presence of a great deal of water soluble high polymers will cause the green sheet to absorb moisture, resulting in increased variations of mechanical characteristics. Furthermore, hydrophobic high polymer latex generated by emulsification and polymerization contains much surfactant; this means a poor workability since it may cause coagulation depending on the type of ceramic powder, and cause foams to be produced during degassing.
On the other hand, when the polymethylmethacrylate resin and polymethacrylic acid ester resin used in (vii) are to be used as organic binder for shaping ceramic, it provides a method of producing the green sheet having a uniform thickness from the slip composed, for example, of ketone solution such as methylethylketone, alcohol solvent such as butyl alcohol, plasticizer, and ceramic powder by the doctor blade method. In this case, all solvents have high steam pressure, and safety against fire is inferior. To ensure safety against fire, conventional techniques have depended on a combined use of halogen solvent, involving environmental pollution problems.